1. Field of the Invention
The present invention relates to an electric device which operates by electric power supplied by a secondary battery, and a method of controlling a power supply circuit which is built in the electric device.
2. Description of the Related Art
The battery voltage of a secondary battery gradually drops as the remaining battery charge decreases. On the other hand, a predetermined required voltage is usually set to a load which operates by electric power supplied by a secondary battery, and it is required to supply electric power in accordance with the required voltage. The required voltage is a voltage which is necessary for the load to normally operate to satisfy the performance specification, and is a specified value determined in advance with respect to the load. Depending on the kinds of the secondary battery and the load, there is a case in which the battery voltage of the secondary battery in a fully charged state exceeds the required voltage of the load, but, when the secondary battery approaches a fully discharged state, the battery voltage of the secondary battery falls below the required voltage of the load. In such a case, a power supply circuit which supplies electric power to the load includes a booster circuit for boosting the battery voltage of the secondary battery so that, even when the battery voltage of the secondary battery drops, the required voltage can be output to the load.